Amazon’s future price-to-earnings (P/E) ratio, based on 2013 profit estimates, has jumped above 100. And the share price has surged 40 percent so far this year.

Despite Amazon’s technology ties, it’s really just a retailer, La Monica says. So it’s hard to justify the lofty valuation. Amazon’s P/E ratio is more than seven times higher than stalwarts Wal-Mart and Target.

And it’s not as if Amazon’s profits are all that hot, he notes. Its net profit margin registered a paltry 0.5 percent in the first half of the year.

“Investors are getting too caught up in the enthusiasm about Amazon's Kindle business and its small but growing cloud services division,” La Monica writes.

“Amazon may not be as much of a bubble as the stock was back in the late 1990s … But it might be getting close.”